Cameras having the capacity to take close-up photographs are not new. An example is the Acmel Macro Auto V6 camera manufactured by Acmel Corporation of Tokyo, Japan. This particular Acmel camera utilizes a plurality of detachable lens assemblies. Each such lens assembly includes a fixed focus lens that, in conjunction with a fixed focus lens located on the camera body, is capable of focusing an image of a relatively close subject at the camera's film plane, with each detachable lens being designed for single subject distance. Each detachable lens assembly also includes a pair of focusing lights employed in the same manner as in the present invention for the purpose of aiding a camera operator to focus a subject image at the camera's film plane. The resulting camera serves its purpose but is altogether too expensive for consumer-type photography and too complicated for easy use by the non-professional. It is both bulky and heavy, weighing about 41/2 pounds.
The use of converging light beams from a camera to determine a proper focal length for the exposure lens is old art as disclosed in U.S. Pat. No. 3,416,426. The theory disclosed therein and in other literature provides a light source reflected from spaced apart mirrors through a lens board to converge at the subject of the photograph. This technique is useful where several parameters remain constant, in particular, one of the constants is flash photography. With flash photography the duration of exposure is set and the only variable is the exposure aperture except of course for the focus of the lens.
The adjustable focus lens Spectra camera sold by Polaroid Corporation of Cambridge, Mass. is an example of where the invention disclosed herein may be incorporated. The Polaroid Corporation presently markets its Spectra camera and a separate attachment for the front thereof, which attachment includes a cover to fit over the subject distance sensing transducer portion of the camera's ultrasonic ranging system. When the ranging system is covered the camera automatically adjusts its focus to a minimum focal position which, in the case of the Spectra camera, is two feet. Focusing the Spectra camera to two feet by this method is one of the features of that particular attachment. Another feature of that attachment is a close-up lens which enables the camera to focus an image of subjects located at a distance of ten (10) inches from the camera. A spring loaded string (ten (10) inches in length) may be pulled from the attachment along a line generally parallel with the axis of the lens system which, in theory, will place the subject in focus. The problem is that the operator must use two hands for the string, attachment and camera in combination and then make sure the camera is not moved after the string is released, before an exposure cycle is initiated. A small deviation of the camera position from the subject as measured by the string will result in a slightly out of focus subject. An appearance design of the adjustable focus lens Spectra camera is shown in U.S. Pat No. De. 279,574 and a focus control system of the type employed in this camera is shown in U.S. Pat. No. 4,291,965.